4. Two inverted conical tanks have their vertices connected by a pipe.
One tank, initially full of water, has a height of 6 feet and a base radius of 3.5 feet.
The other tank, initially empty, has a height of 9 feet and a base radius of 4 feet.

If the water is allowed to flow through the connecting pipe, find the level to which
the water will rise in the empty tank. (Neglect the water in the pipe.)